Chemical Education Today
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Research Advances by Angela G. King
A diet rich in leafy vegetables may minimize the tissue damage caused by heart attacks, according to researchers at the Albert Einstein College of Medicine of Yeshiva University. Their findings suggest that the chemical nitrite, found in many vegetables, could be the secret ingredient in the heart-healthy Mediterranean diet. “Recent studies show that administering nitrite to animals, either intravenously or orally, can greatly limit the damage caused by a heart attack and the stress to tissue that follows due to reperfusion—the return of blood to oxygen-starved heart muscle,” says David Lefer, the study’s senior author and a professor of Medicine and of Pathology at Einstein. “We wondered if feeding animals much lower levels of nitrite and nitrate—equivalent to what people can readily obtain from their diets—could also provide protection from heart-attack injury.” Nitrite and nitrate are important because of their role in producing nitric oxide gas. In 1986, researchers made the remarkable finding that nitric oxide—famous until then mainly as an air pollutant—is produced by cells lining healthy arteries and plays a crucial role in cardiovascular health by dilating arteries and aiding blood flow. NO is produced in vitro by three isoforms of nitric oxide synthase (NOS). Damage to the artery lining (in atherosclerosis and diabetes, for example) impairs nitric oxide production and leads to cardiovascular disease and, ultimately, to heart attacks and strokes. Researchers now have good evidence that hearts undergoing heart attacks have a “backup” pathway for making nitric oxide. Triggered by falling oxygen levels, enzymes in heart muscle convert nitrite stored there into nitric oxide that can then help minimize tissue damage. Nitrite in the diet comes mainly from vegetables— celery, beets, and spinach, lettuce, and other leafy types. Once consumed, nitrite exits the bloodstream and then accumu-
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Image by D. Lefer
Eating Your Greens Could Prove Life-Saving If a Heart Attack Strikes
Figure 1. For seven days mice were fed either standard chow or standard chow supplemented with nitrite water. Then the mice experienced heart attacks and reperfusion. The cross-section of the heart of a mouse fed standard chow, at left, reveals large areas of dead heart muscle (the C-shaped white area). The heart of a mouse that received nitrite water, at right, incurred much less tissue damage (patches of white at top and bottom).
lates and becomes stored in organs such as the heart, kidney, and brain. But it wasn’t clear whether boosting nitrite in the diet could actually translate into better protection from heart-attack damage. To find out, the Einstein researchers administered nitrite (50 mg/liter) in the drinking water of mice for seven days, while a comparison group of mice received a standard diet that was not supplemented with nitrite. Then, to simulate a heart attack, blood flow to the animals’ hearts was stopped for 30 minutes, followed by 24 hours of reperfusion. Examination revealed that the hearts of the nitrite-supplemented mice were significantly richer in nitrite, and heart-muscle damage was reduced by an impressive 48 percent compared with the controls (Figure 1). In contrast to nitrite, nitrate in the diet comes mainly from cured meats such as bacon, sausage, and luncheon meats. Consuming nitrate augments our nitrite supply: Once absorbed in the bloodstream, nitrate circulates to the salivary glands where bacteria convert it to nitrite, which is then swallowed in our saliva. About 10 percent of dietary nitrate is converted to nitrite in this way. As with the mice and nitrite, the Einstein researchers spiked drinking wa-
ter with nitrate and then induced heart attacks. A protective effect was found yet again: Compared with the control animals, the nitrate-supplemented mice had greater stores of nitrite in their heart muscle along with significantly less heartmuscle damage, although the reduction was not as impressive as in the nitrite-fed mice. “This new appreciation of the health benefits of nitrite and nitrate is ironic,” says Lefer, “They’ve traditionally been regarded as toxic because they tend to form chemicals called nitrosamines (RXNO), some of which are carcinogenic. But recent research has found no convincing evidence that nitrite and nitrate pose a cancer risk.” Lefer notes that Europeans’ copious consumption of vegetables puts them far ahead of us in terms of nitrite and nitrate intake: On average, Europeans consume 76 mg of nitrite and nitrate daily compared with a 0.77 mg American intake—nearly a 100-fold difference. “This large intake of nitrite and nitrate poses no known risks and could certainly help explain why the Mediterranean diet is heart-healthy despite its relatively high fat content,” says Lefer. Lefer says that the nitrite levels found cardioprotective in his study can easily be
Journal of Chemical Education • Vol. 85 No. 6 June 2008 • www.JCE.DivCHED.org • © Division of Chemical Education
Chemical Education Today
Reports from Other Journals
More Information
Figure 2. This wood contains a reddish resin called “dragon’s blood”, which shows promise for fighting stomach ulcers.
Photo: Zhizhang Peng
1. Bryan, Nathan S.; Calvert, John W.; Elrod, John W.; Gundewar, Susheel; Ji, Sang Yong; Lefer, David J. Dietary Nitrite Supplementation Protects Against Myocardial Ischemia-Reperfusion Injury. Proc. Nat. Acad. Sci. 2007, 104, 19144–19149. 2. The International Programme on Chemical Safety has published a report on nitrite. See http://www.inchem.org/documents/jecfa/ jecmono/v35je13.htm (accessed Apr 2008). 3. This Journal has previously reported on the potential of nitrite as a therapeutic agent. See J. Chem. Educ. 2004, 81, 934 and 1984, 61, 674. 4. Published undergraduate labs offer experiments for quantifying nitrite in meats and solutions. See J. Chem. Educ. 1973, 50, 426 and 1978, 55, 29.
Photo: Zhizhang Peng
achieved by consuming more vegetables containing the chemical. That dietary change, he says, might be especially helpful for people at increased heart-attack risk—those who’ve already suffered a heart attack, have been diagnosed with cardiovascular disease, or have a family history of it. “Our study suggests that building up nitrite stores in heart muscle could spell the difference between a mild heart attack and one that causes lasting heart damage or death,” says Lefer. “And since nitrite also accumulate in the brain, they could potentially help minimize the damage from strokes as well.”
“Dragon’s Blood” Quenches Stomach Ulcer Bacteria “Dragon’s blood” may sound like an exotic ingredient in a witch’s brew or magic potion. But researchers in China are reporting that the material—which is actually a bright red plant sap used for thousands of years in traditional Chinese medicine—contains chemicals that were effective in laboratory experiments in fighting bacteria that cause millions of cases of gastrointestinal disease each year (Figure 2). In the new study, Weimin Zhao and colleagues indicate that “dragon’s blood” has been used for years in China and other countries as a folk remedy for stomach ulcers, blood clots, and other conditions. Researchers, however, have never identified the active ingredients in dragon’s blood responsible for its beneficial health effects on peptic ulcer and preventing blood clots. The researchers isolated 22 different compounds from the powdered stems of Dracaena cochinchinensis, a common source of dragon’s blood (Figure 3). Eight of the compounds (1–8) have not been previously identified (Figure 4). The powdered air-dried plant stems were extracted with 95% ethanol at room temperature. The solvent was removed and the aqueous residue was partitioned first with chloroform and then with n-butanol. The resulting two fractions were then subjected to column chromatography and HPLC to afford pure compounds. The identity of the pure compounds was established through a combination of mass spectrometry, UV spectroscopy, and NMR spectroscopy.
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Figure 3. Dracaena cochinchinensis, shown above, has been used for thousands of years in Chinese medicine. Now researchers are identifying the chemical basis of its effectiveness.
The scientists tested the compounds’ effects on Helicobacter pylori (H. pylori), the bacteria known to cause most cases of stomach ulcers and gastritis. Two of the new compounds (6 and 7) blocked the growth of H. pylori, with an MIC value of 29.5 μM for both compounds. The compounds were also assayed for thrombin inhibition, involved in blood coagulation, as a measure of their alleged action in promoting circulation. Thrombin is a trypsin-like serine proteinase that catalyzes the conversion of fibrinogen to fibrin as part of the clotting cascade. Many current treatments for thrombosis, or blood clots, involve the inhibition of thrombin, including heparin and coumadin. Compounds 1–7 displayed thrombin inhibitory activity, at moderate levels. Pending significant improvement in their potencies, these compounds are not viable for use in the prevention of the blood clots responsible for some strokes and most heart attacks or as thrombosis treatments, the scientists say, but may offer new leads for investigators to pursue.
Journal of Chemical Education • Vol. 85 No. 6 June 2008 • www.JCE.DivCHED.org • © Division of Chemical Education
Chemical Education Today
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More Information 1. Zhu, Yingdong; Zhang, Ping; Yu, Haiping; Li, Jia; Wang, Ming-Wei; Zhao, Weimin. Anti-Helicobacter pylori and Thrombin Inhibitory Components from Chinese Dragon’s Blood, Dracaena cochinchinensis. J. Nat. Prod. 2007, 70, 1570–1577. 2. For more information on using dragon’s blood to determine ancient trade routes, see J. Chem. Educ. 2004, 81, 1086.
Supporting JCE Online Material
http://www.jce.divched.org/Journal/Issues/2008/Jun/abs764.html Abstract and keywords Full text (PDF) with links to cited URLs and JCE articles
Angela G. King is Senior Lecturer in Chemistry, Wake Forest University, P.O. Box 7486, Winston-Salem, NC 27109;
[email protected].
© Division of Chemical Education • www.JCE.DivCHED.org • Vol. 85 No. 6 June 2008 • Journal of Chemical Education
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